Liquid injection for scavenging

ABSTRACT

Methods are provided for controlling an engine. One method may include boosting engine intake air to a cylinder; and injecting an amount of a scavenging fluid into the cylinder based on an amount of cylinder residual exhaust gas. A scavenging fluid, such as water or windshield washer fluid evaporates on contact with the hot exhaust gases and hot metal components and the expanded volume of the vapor displaces the residual exhaust gas, thereby improving engine scavenging.

CROSS REFERENCE TO RELATED APPLICATIONS

The present application is a continuation of U.S. patent applicationSer. No. 13/748,452, entitled “LIQUID INJECTION FOR SCAVENGING,” filedon Jan. 23, 2013, the entire contents of which are hereby incorporatedby reference for all purposes.

TECHNICAL FIELD

The present application relates to exhaust scavenging for internalcombustion engines.

BACKGROUND AND SUMMARY

Exhaust scavenging in internal combustion engines is used to clear hotexhaust products from a combustion cylinder and recharge the cylinderwith fresh intake air. Scavenging allows fresh air to flush out most ofthe residual hot exhaust gas from the clearance volume, and theresulting decrease in temperature reduces knock tendency, thus allowinggreater spark advance which increases torque. Furthermore, the reductionin the amount of residual exhaust gas leaves more room for freshair-fuel mixture which further increases torque. Scavenging is commonlyused in the European market, but most turbocharged engines sold in theUS market are calibrated to use much less scavenging, due to emissionsconcerns.

Traditional scavenging, or “blow through”, of fresh air is used when theintake manifold pressure is higher than exhaust manifold pressure. Thisis typical of turbocharged engines up to approximately 2000-2500 RPM.Turbocharged engines with tiVCT (Twin Independent Variable CamshaftTiming) can achieve low speed knock and torque benefits usingscavenging. However, traditional scavenging can result in oxygenatedfresh air passing through the exhaust valve and on to the exhaustaftertreatment system, resulting in increased emissions. The excess ofoxygen in the exhaust is, in part, due to air flow used for traditionalexhaust scavenging flowing through the exhaust valve during valveoverlap. In some instances, this overlap allows intake air directly intothe exhaust before the combustion stroke occurs. This unburned oxygenmakes its way into the exhaust and can alter the chemistry of exhaustgas aftertreatment catalysts. In particular, increased oxygen lessenscatalyst reducing ability thus decreasing the reduction of nitrogenoxides (NO_(x)) prior to venting exhaust gases to the atmosphere.Furthermore, traditional scavenging relies on a pressure decrease fromintake manifold to exhaust manifold in order to drive scavenging airflow through the cylinder. Under some operating conditions, thispressure differential is not present, decreasing the window ofopportunity for exhaust scavenging.

The present disclosure describes a system and method for injection of ascavenging fluid, such as water or windshield washer fluid, directlyinto the cylinder, or via port injection, for vapor scavenging which canbe achieved without excess oxygen to the exhaust system. The injectedliquid evaporates quickly in the high temperature residual exhaust gasand/or when droplets impinge on hot metal surfaces in the combustionchamber. A relatively small amount of liquid can evaporate into arelatively large volume of vapor, thus displacing the residual exhaustgas and forcing it out the open exhaust valves. The use of vapor forscavenging reduces intake air released through the exhaust valve whencompared to traditional scavenging that utilizes air flow across apressure differential to displace residual exhaust gas. Furthermore,because the present disclosure relies on the expansion of liquid tovapor to displace the residual exhaust gas, vapor scavenging can occureven when intake manifold pressure is lower than exhaust manifoldpressure. This method is adaptable to port injection or direct injectionand may be compatible with various fuels, including diesel, gasoline,and ethanol as examples.

The disclosure describes a method for an engine comprising, injecting anamount of one of water and windshield washer fluid into a combustioncylinder based on a density and volume of residual exhaust gas. Portinjection or direct injection scavenging with water or windshield washerfluid can reduce emissions concerns due to excessive oxygen in theexhaust aftertreatment system. Unlike traditional scavenging, the methodof the present disclosure can also be used on engines without tiVCT, andeven when intake manifold pressure is lower than exhaust pressure, suchas at higher RPM, or at low RPM and medium-high load when knock is aconcern. Furthermore, vapor scavenging may reduce the temperature of acombustion cylinder and thus reduce knock.

The above advantages and other advantages, and features of the presentdescription will be readily apparent from the following DetailedDescription when taken alone or in connection with the accompanyingdrawings.

It should be understood that the summary above is provided to introducein simplified form a selection of concepts that are further described inthe detailed description. It is not meant to identify key or essentialfeatures of the claimed subject matter, the scope of which is defineduniquely by the claims that follow the detailed description.Furthermore, the claimed subject matter is not limited toimplementations that solve any disadvantages noted above or in any partof this disclosure. Further, the inventors herein have recognized thedisadvantages noted herein, and do not admit them as known.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows an example cylinder of an internal combustion engine.

FIG. 2 shows a flow chart depicting a method of injecting scavengingfluid.

FIG. 3 shows scavenging fluid injection timing for port and directinjection.

FIG. 4 shows a flowchart depicting adjustments to the amount ofscavenging fluid injected.

FIG. 5 shows a flowchart depicting an embodiment of the method whereinthe engine is equipped with variable valve timing.

DETAILED DESCRIPTION

The present disclosure details injection of a liquid for vaporscavenging. In one embodiment scavenging fluid is direct injected latein the exhaust stroke. In an alternate embodiment, employing portinjection, fluid is injected during valve overlap or just before theintake stroke. With port injection into the intake air passage, liquidor vapor is readily taken in through the intake valve where it functionsin the same way as directly injected fluid. In both embodiments, liquidis quickly evaporated as it hits hot residual gases or hot surfaces. Asmall amount of liquid expands as it evaporates and displaces theresidual exhaust gas, forcing it past the open exhaust valve or valves.Heat is removed from the hot cylinder both by displacing hot residualexhaust products and through evaporative cooling. In this way, injectionof scavenging fluid may also reduce propensity for knock and the methodof the present disclosure can be adapted for knock mitigation.Furthermore, the present disclosure can be utilized in an engine with orwithout variable valve timing and even when intake manifold pressure islower than exhaust manifold pressure.

The system and method of the present disclosure are described below inreference to the figures. FIG. 1 shows an example cylinder of an enginein accordance with the present disclosure. FIG. 2 details a method ofthe present disclosure in the form of a flow chart. FIG. 3 diagramsinjection timing. FIG. 4 depicts adjustment of a quantity of scavengingfluid injected in response to various feedback from engine sensors. FIG.5 diagrams a method in accordance with the present disclosure as itpertains to an engine equipped with variable valve timing.

FIG. 1 depicts an example embodiment of a combustion chamber or cylinderof internal combustion engine 10. Engine 10 may receive controlparameters from a control system including controller 12 and input froma vehicle operator 130 via an input device 132. In this example, inputdevice 132 includes an accelerator pedal and a pedal position sensor 134for generating a proportional pedal position signal PP. Cylinder (hereinalso “combustion chamber’) 14 of engine 10 may include combustionchamber walls 136 with piston 138 positioned therein. Piston 138 may becoupled to crankshaft 140 so that reciprocating motion of the piston istranslated into rotational motion of the crankshaft. Crankshaft 140 maybe coupled to at least one drive wheel of the passenger vehicle via atransmission system. Further, a starter motor may be coupled tocrankshaft 140 via a flywheel to enable a starting operation of engine10.

Cylinder 14 can receive intake air via a series of intake air passages142, 144, and 146. Intake air passage 146 may communicate with othercylinders of engine 10 in addition to cylinder 14. In some embodiments,one or more of the intake passages may include a boosting device such asa turbocharger or a supercharger. For example, FIG. 1 shows engine 10configured with a turbocharger including a compressor 174 arrangedbetween intake passages 142 and 144, and an exhaust turbine 176 arrangedalong exhaust passage 148. Compressor 174 may be at least partiallypowered by exhaust turbine 176 via a shaft 180 where the boosting deviceis configured as a turbocharger. However, in other examples, such aswhere engine 10 is provided with a supercharger, exhaust turbine 176 maybe optionally omitted, where compressor 174 may be powered by mechanicalinput from a motor or the engine. A throttle 162 including a throttleplate 164 may be provided along an intake passage of the engine forvarying the flow rate and/or pressure of intake air provided to theengine cylinders. For example, throttle 162 may be disposed downstreamof compressor 174 as shown in FIG. 1, or alternatively may be providedupstream of compressor 174.

Exhaust passage 148 may receive exhaust gases from other cylinders ofengine 10 in addition to cylinder 14. Exhaust gas sensor 128 is showncoupled to exhaust temperature sensor 129 and exhaust constituent sensor127 off exhaust passage 148 upstream of emission control device 178. Inan alternate embodiment, these sensors may not be located adjacent toone another and may be dispersed through exhaust passage 148. Sensor 128may be selected from among various suitable sensors for providing anindication of exhaust gas air/fuel ratio such as a linear oxygen sensoror UEGO (universal or wide-range exhaust gas oxygen), a two-state oxygensensor or EGO (as depicted), a HEGO (heated EGO), a NOx, HC, or COsensor, for example. Emission control device 178 may be a three waycatalyst (TWC), NOx trap, various other emission control devices, orcombinations thereof. Exhaust gas sensor 128, exhaust temperature sensor129 and exhaust constituent sensor 127 provide input to controller 12via input/output ports 108.

Exhaust temperature may be measured by one or more temperature sensorssuch as exhaust temperature sensor 129 located in exhaust passage 148.Alternatively, exhaust temperature may be inferred based on engineoperating conditions such as speed, load, air-fuel ratio (AFR), sparkretard, etc. Further, exhaust temperature may be computed by one or moreexhaust gas sensors 128. It may be appreciated that the exhaust gastemperature may alternatively be estimated by any combination oftemperature estimation methods listed herein.

Each cylinder of engine 10 may include one or more intake valves and oneor more exhaust valves. For example, cylinder 14 is shown including atleast one intake poppet valve 150 and at least one exhaust poppet valve156 located at an upper region of cylinder 14. In some embodiments, eachcylinder of engine 10, including cylinder 14, may include at least twointake poppet valves and at least two exhaust poppet valves located atan upper region of the cylinder.

Intake valve 150 may be controlled by controller 12 by cam actuation viacam actuation system 151. Similarly, exhaust valve 156 may be controlledby controller 12 via cam actuation system 153. Cam actuation systems 151and 153 may each include one or more cams and may utilize some form ofvariable valve timing (VVT) such as one or more of cam profile switching(CPS), variable cam timing (VCT), such as twin independent variable camtiming (tiVCT), and/or variable valve lift (VVL) systems that may beoperated by controller 12 to vary valve operation. The operation ofintake valve 150 and exhaust valve 156 may be determined by valveposition sensors (not shown) and/or camshaft position sensors 155 and157, respectively. In alternative embodiments, the intake and/or exhaustvalve may be controlled by electric valve actuation. For example,cylinder 14 may alternatively include an intake valve controlled viaelectric valve actuation and an exhaust valve controlled via camactuation including CPS and/or VCT systems.

In some embodiments, each cylinder of engine 10 may include a spark plug192 for initiating combustion. Ignition system 190 can provide anignition spark to combustion chamber 14 via spark plug 192 in responseto spark advance signal SA from controller 12, under select operatingmodes. However, in some embodiments, spark plug 192 may be omitted, suchas where engine 10 may initiate combustion by auto-ignition or byinjection of fuel as may be the case with some diesel engines.

In some embodiments, each cylinder of engine 10 may be configured withone or more injectors for providing a scavenging fluid thereto. As anon-limiting example, cylinder 14 is shown including one fuel injector166. Fuel injector 166 is shown coupled directly to cylinder 14 forinjecting fuel directly therein in proportion to the pulse width ofsignal FPW received from controller 12 via electronic driver 168. Inthis manner, fuel injector 166 provides what is known as directinjection (hereafter also referred to as “DI”) of fuel into combustioncylinder 14. While FIG. 1 shows injector 166 as a side injector, it mayalso be located overhead of the piston, such as near the position ofspark plug 192. Fuel may be delivered to fuel injector 166 from a highpressure fuel system 8 including fuel tanks, fuel pumps, and a fuelrail. Alternatively, fuel may be delivered by a single stage fuel pumpat lower pressure, in which case the timing of the direct fuel injectionmay be more limited during the compression stroke than if a highpressure fuel system is used. Further, while not shown, the fuel tanksmay have a pressure transducer providing a signal to controller 12. Itwill be appreciated that, in an alternate embodiment, injector 166 maybe a port injector 170, indicated as a variation in dotted line,providing fuel into the intake port upstream of cylinder 14. Both directinjector 166 and the variation, port injector 170, could be configuredto also inject a scavenging fluid such as water or windshield washerfluid from scavenging fluid reservoir 9. In the case of port injectionof scavenging fluid a spray of the injection fluid is aimed at a valve,in the direction of the cylinder such that when the intake valve opensspray is aimed past the open valve, at least partially into thecylinder. Alternatively a scavenging fluid injection device may bespaced apart from the fuel injector and arranged to either directlyinject or port inject a scavenging fluid.

Fuel may be delivered by the injector to the cylinder during a singlecycle of the cylinder. Further, the distribution and/or relative amountof fuel or scavenging fluid delivered from the injector may vary withoperating conditions, such as aircharge temperature, or residual exhaustgas volume and density, as described herein below. Furthermore, for asingle combustion event, multiple injections of the delivered fuel maybe performed per cycle. The multiple injections may be performed duringthe compression stroke, intake stroke, or any appropriate combinationthereof.

As described above, FIG. 1 shows one cylinder of a multi-cylinderengine. As such each cylinder may similarly include its own set ofintake/exhaust valves, fuel injector(s), scavenging fluid injectiondevice, spark plug, etc.

Controller 12 is shown in FIG. 1 as a microcomputer, includingmicroprocessor unit 106, input/output ports 108, an electronic storagemedium for executable programs and calibration values shown as read onlymemory chip 110 in this particular example, random access memory 112,keep alive memory 114, and a data bus. Controller 12 may receive varioussignals from sensors coupled to engine 10, in addition to those signalspreviously discussed, including measurement of inducted mass air flow(MAF) from mass air flow sensor 122; engine coolant temperature (ECT)from temperature sensor 116 coupled to cooling sleeve 118; a profileignition pickup signal (PIP) from Hall effect sensor 120 (or other type)coupled to crankshaft 140; throttle position (TP) from a throttleposition sensor; manifold absolute pressure signal (MAP) from sensor124; and knock signal (KS) from knock sensor 181. Knock sensor 181 mayalternatively be located on the cylinder head or may be a sensor todetect vibrations from knock in crankshaft 140. Engine speed signal,RPM, may be generated by controller 12 from signal PIP. Manifoldpressure signal MAP from a manifold pressure sensor may be used toprovide an indication of vacuum, or pressure, in the intake manifold.Still other sensors may include fuel level sensors and fuel compositionsensors coupled to the fuel tank(s) of the fuel system.

Storage medium read-only memory 110 can be programmed with computerreadable data representing instructions executable by processor 106 forperforming the methods described below as well as other variants thatare anticipated but not specifically listed.

FIG. 2 shows a flowchart depicting a method 200 in accordance with thepresent disclosure. The method 200 may be carried out by enginecontroller 12. At 202, the amount of the residual exhaust gas incylinder 14 is estimated or measured. The amount of residual exhaust gasmay be based on estimates of density and volume which may be computed bycontroller 12 based on inputs from MAP sensor 124, temperature sensor116, exhaust temperature sensor 129, or based on operating conditionssuch as air-fuel ratio, load, speed, etc. . . . . The temperature andpressure of the residual exhaust gas may be used to calculate thedensity of residual exhaust gas. The volume of residual exhaust gas maybe estimated based on engine operating conditions and other inputs. At204, the density and volume of residual exhaust gas may be used tocalculate the amount of fluid injected. The amount of fluid to beinjected will vary with the amount of the residual exhaust gas as theforce of gas pressure needed to expel differing amounts of residualexhaust gas from cylinder 14 differs. The amount of fluid injectedincreases with the amount of residual exhaust gas present in thecylinder. Adjusting the amount of fluid injection based on thecalculated amount of residual exhaust gas may limit excessiveconsumption of scavenging fluid. Furthermore, if the amount of residualexhaust gas is below a threshold, no injection of scavenging fluid mayoccur. The amount of scavenging fluid injected by port injection can beestimated in substantially the same way.

At 206, it is determined if the engine load is greater than an upperthreshold. If the engine load is not greater than an upper threshold (NOat 206) the method proceeds to 208 where no scavenging fluid is injecteduntil the engine load is greater than an upper threshold. If at 206, theengine load is greater than an upper threshold (YES) the method proceedsto 210.

At 210, it is determined if the engine is knock-limited. If at 210, theengine is not knock-limited (NO) the method proceeds to 212 where noinjection of scavenging fluid occurs until the engine is knock-limited.If at 210, the engine is knock-limited (YES) the method proceeds to 214.

At 214, it is determined if the extent of valve overlap is below apredetermined threshold. If the extent of valve overlap is not below thepredetermined threshold (NO) the method proceeds to 216 where noscavenging fluid is injected until valve overlap is below the threshold.If valve overlap is below threshold (YES at 214), the method proceeds to218.

Injection of scavenging fluid may occur in the presence of some valveoverlap, and in fact port injection of scavenging fluid may occur duringvalve overlap. Adjustments to variable valve timing may be made togenerate some valve overlap below the threshold if injection ofscavenging fluid is to be used.

At 218, it is determined if the time is the selected injection time. Ifit is not the selected injection time (NO at 218) the method proceeds to220 where there is no injection of scavenging fluid until the time hasreached the selected injection time. The selected injection time isdetermined by the type of injection. If scavenging fluid is directinjected, such as by direct injector 166, the injection of scavengingfluid may occur late in the exhaust stroke. Direct injection of water orwindshield washer fluid late in the exhaust stroke cannot be too early,or the amount of residual exhaust gas will be higher and more fluid willbe required. Also, it cannot be too late, or the fluid won't have timeto completely evaporate and displace residual gas before the intakevalves open. For port injection, such as by port injector 170, injectionof scavenging fluid may occur during valve overlap, when the intakevalve 150 is open very early in the intake stroke, or even when theintake valve 150 is closed just before the intake stroke. The liquid orvapor enters the cylinder 14 through the open intake valve to achievevapor scavenging in a way similar to that of directly injected fluid.The timing constraints on port injection of water or windshield washerfluid are not as severe. Early injection has little penalty, so a simplecontrol algorithm could be used, for example to keep start of ignition(SOI) or end of ignition (EOI) at or near intake valve opening timing,or a fixed offset from it.

Precise controls may lead to a successful implementation of the method.The injection timing and amount are both controlled to achieve a balancebetween sufficient scavenging and excess consumption of scavengingfluid.

If at 218, the time is the selected injection timing (YES) the methodproceeds to 222 where scavenging fluid is injected either directly intothe cylinder 14 or port injected into the intake air passage 146. Themethod then proceeds to 224 where feedback is provided to controller 12regarding the injection of scavenging fluid. Method 400 of FIG. 4provides detail on feedback provided to engine controller 12 based onthe injection and subsequent adjustment of future injection fluidamount. Additionally, feedback on temperature and pressure as estimatedor measured by MAP sensor 124 or temperature sensor 116, may also beprovided and utilized in the adjustment of timing of the injection or toindicate if scavenging fluid has run out or scavenging injection hasotherwise failed. After feedback on the injection of fluid is providedto engine controller 12 at 224 the method 200 then returns.

FIG. 3 illustrates the timing of scavenging fluid injection by directinjection. At 300, valve overlap 301 is below a threshold and injectionof scavenging fluid occurs. This is in contrast to 310 where valveoverlap 311 is not below a threshold and no injection of scavengingfluid occurs. At 302, exhaust and intake valve opening with low overlap301 are indicated for two combustion cycles. At 304, fuel injection istimed early in the intake stroke following exhaust valve closure.Injection of scavenging fluid, be it water or windshield washer fluid,is seen at 306. Scavenging fluid injection is timed in the second halfof the exhaust stroke prior to intake valve opening for direct injectionof scavenging fluid. Scavenging fluid injection may occur in the secondhalf of the exhaust stroke after combustion is more than 90% completed.This timing, immediately prior to intake valve opening, may also beeffective for port injection of scavenging fluid. Port injection ofscavenging fluid may also occur during valve overlap.

Indicated generally at 310 is the converse situation where scavengingfluid is not injected because valve overlap is not below a threshold.Opening of the exhaust and intake valves with valve overlap 311 notbelow a threshold is seen at 312. At 314, the injection of fuel is shownearly in the intake stroke after the exhaust valve has closed. Noinjection of scavenging fluid is shown at 316 as valve overlap is notbelow a threshold.

FIG. 4 details a method for adjusting the amount of scavenging fluidinjected based on feedback from a prior injection of scavenging fluid.The method 400 starts at 402 where the method 200 of FIG. 2 isperformed. At 404 the last step, 212, of method 200 is elaborated on.Feedback is provided to engine controller 12 based on the priorscavenging fluid injection. This feedback may include input from a knocksensor 181, exhaust oxygen sensor such as exhaust gas sensor 128,exhaust temperature sensor 129, or exhaust constituent sensor 127. Insome embodiments all of these sensors may not be present, and feedbackmay be provided from existing sensors or based on estimations by enginecontroller 12 based on engine operating conditions.

If at 406, knock in excess of threshold is detected by knock sensor 181(YES), the amount of scavenging fluid in the following injection isincreased at 408 in order to further scavenge and cool the cylinder andhelp prevent knock. If NO at 406, the method proceeds to 410 where it isdetermined if exhaust oxygen content is higher than threshold asdetected by exhaust oxygen sensor 128. If the exhaust temperature ishigher than threshold at 410 (YES) the amount of fluid injected in thefollowing injection is increased at 412 to further scavenge thecombustion chamber, thus avoiding excess oxygen in the catalyst andreducing NO_(x) emissions.

If at 410, the exhaust oxygen content is not above the threshold, themethod 400 proceeds to 414 where it is determined if the exhausttemperature is above a threshold. If the exhaust temperature is above athreshold (YES) the amount of scavenging fluid in the followinginjection is increased at 416 to further scavenge and cool the cylinderand ultimately cool exhaust products.

If at 414, the exhaust temperature is not above a threshold the methodproceeds to 418 where it is determined if a constituent in the exhaustis above a threshold. An exhaust constituent sensor such as constituentsensor 127 may be utilized to indicate if excessive scavenging fluid orits vapor components is present in the exhaust. The exhaust constituentsensor could, for example, detect water vapor, methanol vapor, or someother component of the scavenging fluid. If the constituent level isabove a threshold at 418 (YES) the amount of fluid injected in thefollowing scavenging fluid injection is decreased at 420 to avoidexcessive consumption of scavenging fluid. The method 400 then returns.

It should be understood that though listed sequentially the steps 406,410, 414 and 420 may occur in a varied order or simultaneously. Inaddition, adjustments to the amount of scavenging fluid injected may beadditive. For example, if at 414 exhaust temperature is above athreshold and at 406, knock is above a threshold the increase to theamount of fluid injected may be greater than if either high exhausttemperature or knock was detected on its own. Also, thoughsimplistically described as a single threshold here, each detection mayhave multiple thresholds corresponding to differing magnitude adjustmentto the amount of fluid injected. Furthermore, additional sensors, notlisted above may be present and used to provide feedback in order tocontrol injection amount or timing for vapor scavenging. In addition tofeedback from specific sensors, adjustments to the injection may be madeon estimates of exhaust properties based on engine operating conditionssuch as MAP, engine speed, air-fuel ratio, etc.

Exhaust scavenging by a method of the present disclosure can increasetorque by allowing for spark advance by virtue of a decreased cylindertemperature or by clearing the combustion chamber of exhaust residualsallowing more room for fresh air-fuel mixture. Furthermore, injection ofscavenging fluid can prevent or mitigate knock and/or pre-ignition.Precise control of the quantity of fluid injected in response to theabovementioned feedback confers various advantages to a method inaccordance with the present disclosure. Injection timing may be timedwith valve overlap, injecting at the right time and with valve overlapbelow a threshold may ensure success of scavenging fluid injection,diminishing emissions and increasing positive effects of exhaustscavenging by a method of the present disclosure. Further, controllingthe amount of fluid injected responsive to various feedback may ensurethat exhaust scavenging is effective while minimizing the amount offluid needed, preserving fluid for future injection and preventing buildup of scavenging liquid or vapor in a cylinder, oil sump, or exhaustsystem.

In reference to FIG. 5, an embodiment of a method 500 for controllinginjection of scavenging fluid in an engine equipped with variable valvetiming (VVT) is described. The engine 10, of FIG. 1, may be compatiblewith the method 500 if cam actuation systems 151 and 153 include, forexample, twin independent variable camshaft timing (tiVCT) and/or camprofile switching (CPS) and/or variable valve lift (VVL). In the method500 valve timing may be coordinated with injection of scavenging fluid.At 502 it is assessed if scavenging by fluid injection is occurring. IfYES at 502, injection of scavenging fluid is carried out according tothe method 200 of FIG. 2 with the additional coordination of VVT at 504.Coordination of VVT with scavenging injection includes controlling valvetiming for low overlap and low trapped volume (e.g. exhaust valveclosure near top dead center). If scavenging by fluid injection is notoccurring (NO at 502) the method then proceeds to 506. Injection byscavenging fluid might not occur in situations of a system error or ifit is detected that the fluid level reservoir 9 containing one of waterand windshield washer fluid is below a threshold level. At 506, in theabsence of scavenging by fluid injection VVT is controlled to avoidknock. This may include retarding intake valve closure and/or limiteduse of traditional exhaust scavenging which uses positive pressure fromthe intake manifold to blow residual exhaust gases through the exhaustvalve opening. At 508, it is assessed if knock avoidance was successfulby determining if knock is greater than a threshold value. This may bedetermined by knock sensor 181. If knock is not greater than threshold(NO at 508) the method then returns. If knock is greater than threshold(YES at 508) additional knock mitigation steps are performed at 510.These may include reducing boost in a boosted engine, and/or retardingspark ignition in a spark ignition engine. It should be understood theseare merely examples of additional knock mitigation steps and the methodsand system of the present disclosure may be carried out in non-boostedengines, and/or engines without spark ignition. Furthermore an enginewithout VVT may use spark retard or reduced boost to mitigate knock ifscavenging fluid injection errs or is insufficient to prevent knock.Furthermore, though the method 500 describes a method specific to anembodiment in which the engine is equipped with VVT, it should beunderstood that VVT is not necessary for vapor scavenging and anadvantage of the present disclosure is its adaptability to engines withor without VVT.

The present disclosure describes a method, comprising: boosting engineintake air to a cylinder; and injecting an amount of one of water andwindshield washer fluid into the cylinder based on an amount of residualexhaust gas. The water or windshield washer fluid evaporate on contactwith the hot exhaust gases and hot metal components and the expandedvolume of the vapor displaces the residual exhaust gas. The method isadaptable to direct or port injection and can be used with or withoutvariable cam timing and even when intake manifold pressure is higherthan exhaust manifold pressure.

It will be appreciated that the configurations and methods disclosedherein are exemplary in nature, and that these specific embodiments arenot to be considered in a limiting sense, because numerous variationsare possible. For example, the above technology can be applied to V-6,I-4, I-6, V-12, opposed 4, and other engine types. The subject matter ofthe present disclosure includes all novel and non-obvious combinationsand sub-combinations of the various systems and configurations, andother features, functions, and/or properties disclosed herein.

The following claims particularly point out certain combinations andsub-combinations regarded as novel and non-obvious. These claims mayrefer to “an” element or “a first” element or the equivalent thereof.Such claims should be understood to include incorporation of one or moresuch elements, neither requiring nor excluding two or more suchelements. Other combinations and sub-combinations of the disclosedfeatures, functions, elements, and/or properties may be claimed throughamendment of the present claims or through presentation of new claims inthis or a related application. Such claims, whether broader, narrower,equal, or different in scope to the original claims, also are regardedas included within the subject matter of the present disclosure.

The invention claimed is:
 1. A method, comprising: boosting engineintake air to a cylinder; initiating combustion with a spark plug; andinjecting an amount of a scavenging fluid into the cylinder based on anamount of cylinder residual exhaust gas.
 2. The method of claim 1,further comprising taking mitigating action in response to knock.
 3. Themethod of claim 2, wherein the mitigating action includes reducingboost.
 4. The method of claim 2, wherein the mitigating action includesretarding spark timing.
 5. The method of claim 2, wherein the scavengingfluid is one of water and windshield washer fluid.
 6. The method ofclaim 5, wherein injecting the amount of one of water and windshieldwasher fluid into the cylinder is via a direct injector.
 7. The methodof claim 5, wherein injecting the amount of one of water and windshieldwasher fluid further comprises injecting the amount of one of water andwindshield washer fluid in a second half of an exhaust stroke.
 8. Themethod of claim 5, wherein injecting the amount of one of water andwindshield washer fluid into the cylinder is via a port injector.
 9. Themethod of claim 8, wherein injecting the amount of one of water andwindshield washer fluid further comprises injecting the amount of one ofwater and windshield washer fluid during valve overlap, an injectionspray aimed past an open valve at least partially into the cylinder. 10.The method of claim 8, wherein injecting the amount of one of water andwindshield washer fluid further comprises injecting the amount of one ofwater and windshield washer fluid at an end of an exhaust strokeimmediately prior to an intake stroke and intake valve opening.
 11. Themethod of claim 5, wherein water is injected via a direct injector in asecond half of an exhaust stroke after combustion is more than 90%completed, the injected water vaporizing in the cylinder and pushingadditional cylinder residual exhaust gas past an open exhaust valve, thewater injected responsive to the amount of residual exhaust gas beinggreater than a threshold, and an extent of valve overlap of an intakeand an exhaust valve being below a threshold.
 12. The method of claim 5,wherein the amount of one of water and windshield washer fluid isincreased responsive to an increased amount of residual exhaust gas, andfurther increased responsive to knock.
 13. A method, comprising: ifvalve overlap is below a threshold, injecting an amount of one of waterand windshield washer fluid into a cylinder operating with boost duringan exhaust stroke to increase scavenging; and if valve overlap is abovea threshold, not injecting one of water and windshield washer fluid intothe cylinder during the exhaust stroke.
 14. The method of claim 13,further comprising, initiation combustion in the cylinder with sparkignition.
 15. The method of claim 14, further comprising boosting engineintake air to the cylinder above exhaust pressure with valve overlapbelow the threshold, and adjusting variable valve timing to generate atleast some valve overlap below the threshold.
 16. The method of claim13, further comprising, wherein an engine carries out combustion of afuel other than one of water and windshield washer fluid in a cylindercycle of the exhaust stroke, where said scavenging is performed atengine loads above an upper threshold where the engine is knock-limited.17. The method of claim 16, further comprising, adjusting variable valvetiming to retard intake valve closure when a fluid level in a reservoircontaining one of water and windshield washer fluid is below a thresholdand knock is detected.
 18. The method of claim 15, further comprising,reducing the boosting of engine intake air when a fluid level in areservoir containing one of water and windshield washer fluid is below athreshold and knock is detected.
 19. The method of claim 15, furthercomprising, retarding spark ignition when a fluid level in a reservoircontaining one of water and windshield washer fluid is below a thresholdand knock is detected, and adjusting the amount of one of water andwindshield washer fluid injected into the cylinder based on an amount ofresidual exhaust gas.
 20. An engine method, comprising: injecting anamount of fluid into a cylinder, the amount based on density and volumeof residual exhaust gas in the cylinder, the fluid comprising water;initiating combustion in the cylinder via a spark plug; and adjustingthe amount based on feedback from an engine sensor.